It is known to use a layer of foam as a temporary blanket or cover over hazardous material spills. Persistent foams are taught, for example, in U.S. Pat. No. 5,434,192 to suppress the release of hydrocarbon and polar organic vapors during loading of oil tankers, as well as during the transportation, transfer, storage and accidental storage and accidental spillage or crude oil and the like. Aqueous foamable compositions for fighting fires on hydrophobic or hydrophilic liquids are disclosed in U.S. Pat. No. 4,060,489. Each of the two foregoing U.S. patents is incorporated herein by reference in its entirety. Aqueous film-forming foam (AFFF) compositions and other fire fighting foam compositions (such as protein, fluoroprotein and synthetic detergents), referred to here in some cases as aqueous foamable concentrates, are known for these and other applications. Improved compositions are required, however, for treating liquid hazardous waste spills, especially spills of non-neutral pH liquid hazardous materials, that is, spills of acidic or caustic liquids, and especially workplace spills. The paper industry is under pressure to substitute chlorine dioxide for aqueous solution chlorine in paper production processes. Chlorine dioxide is slightly (typically up to about 13%) soluble in water to produce a highly acidic liquid, which decomposes violently, liberating heat, chlorine gas and nascent oxygen. When aqueous chlorine dioxide solution is spilled, noxious vapor of chlorine dioxide gas is readily liberated to the atmosphere. Agitation of spilled chlorine dioxide solution can cause increased release of vapors to the atmosphere. Spraying with water can cause such undesirable agitation and, in addition, can cause an unwanted temperature increase in the spilled material, with consequent increased vapor release, due to heat of reaction released during rapid mixing of the spray water with the acidic chlorine dioxide solution. Likewise, certain aqueous foams breakdown too rapidly over chlorine dioxide spills or other non-neutral pH liquids, thereby causing rapid heating and vapor release. More persistent foams, while avoiding such undesirable heating of the spilled non-neutral pH liquid, may merely blanket the spill and, perhaps, even inhibit effective access for treatment and clean up.
In view of the foregoing difficulties, strongly acidic liquids, such as chlorine dioxide solution spills, cannot always be effectively treated with current methods. Agents such as known aqueous film-forming foams tend to be too rapidly broken down upon application to such spills, potentially causing excessive heating and increased vapor release and requiring application of an undesirable number of additional layers to maintain an unbroken foam blanket over the spill. In addition, treatment employing certain known AFFFs is unsatisfactory, as chlorine dioxide has been reported to have violent reactions with materials frequently employed in such formulations, such as sugar, sulfur, fluorine and difluroamine.
As noted above, foam stability can be an important consideration for treating acidic or caustic spills. Heating of the hazardous liquid due to the exothermic neutralization reaction can be high enough to raise the temperature of the spilled liquid sufficiently to cause substantial increase in vapor release and deterioration of the foam blanket. Three factors have been suggested to control foam stability. In the first stage of foam life, water drainage may primarily control foam stability. As water drains from the foam films or lamellae, the films thin quickly to a small thickness. In a subsequent stage of foam decay, the bubbles slowly begin to collapse or coalesce into fewer, but larger bubbles. Gas diffusion and, more importantly, water evaporation from the foam lamellae may be the primary cause of foam collapse during this stage. In a final or near final stage, foam lamellae becomes so thin that even small pertabations, such as vibrations, shocks or sudden pressure or temperature changes can cause the remaining foam columns to collapse catastrophically, resulting in breaks or breaches in the foam blanket.
Accordingly, it is an object of the present invention to provide treatment methods and materials to address the problems set forth above. It is a particular object of the invention to provide methods and materials for treatment of hazardous materials spills, especially non-neutral pH liquids, for example chlorine dioxide solutions and other fuming acids and bases. These and other objects and features of the invention will be readily apparent from the following disclosure and Detailed Description of Certain Preferred Embodiments.